1. Technical Field
The present disclosure generally relates to a surgical apparatus for fusing adjacent bone structures, and, more particularly, to an apparatus and associated method for fusing adjacent vertebrae.
2. Background of the Related Art
The fusion of adjacent bone structures is commonly performed to provide for long-term replacement to compensate for degenerative or deteriorated disorders in bone. For example, an intervertebral disc, which is a ligamentous cushion disposed between adjacent vertebrae, may undergo deterioration as a result of injury, disease, tumor or other disorders. The disk shrinks or flattens leading to mechanical instability and painful disc translocations.
Conventional procedures for disc surgery include partial or total excision of the injured disc portion, e.g., discectomy, and replacement of the excised disc with biologically acceptable plugs or bone wedges. The plugs are driven between adjacent vertebrae to maintain normal intervertebral spacing and to achieve, over a period of time, bony fusion with the plug and opposed vertebrae. More recently, emphasis has been placed on fusing bone structures (i.e., adjoining vertebrae) with metallic or ceramic prosthetic cage implants. One fusion cage implant is disclosed in commonly assigned U.S. Pat. No. 5,026,373 to Ray et al., the contents of which are incorporated herein by reference. The Ray ""373 fusion cage includes a cylindrical cage body having a thread formed as part of its external surface and apertures extending through its wall which communicate with an internal cavity of the cage body. The fusion cage is inserted within a tapped bore or channel formed in the intervertebral space thereby stabilizing the vertebrae and maintaining a pre-defined intervertebral space. Preferably, a pair of fusion cages are implanted within the intervertebral space. The adjacent vertebral bone structures communicate through the apertures and with bone growth inducing substances which are within the internal cavity to unite and eventually form a solid fusion of the adjacent vertebrae. FIGS. 1-2 illustrate the insertion of a pair of the Ray ""373 fusion cages positioned within an intervertebral space.
Accordingly, the present invention is directed to further improvements in spinal fusion procedures. In accordance with a preferred embodiment, an apparatus for facilitating fusion of adjacent bony structures includes an outer implant member with an implant wall having outer and inner wall surfaces and defining an internal cavity and an inner implant member at least partially disposed within the internal cavity of the outer implant member and adapted for movement relative thereto. The inner implant member includes an implant wall having outer and inner wall surfaces and defining at least one locking slot portion therein. The apparatus further includes a locking clip which is mountable to the outer wall surface of one of the outer and inner implant members. The locking clip includes a locking arm arranged for reception within the one locking slot of the inner member and being dimensioned to engage the outer wall of the outer member to secure a relative position of the inner and outer members. The locking clip may further include a clip base and opposed locking arms depending from the base. The opposed locking arms are dimensioned for reception within corresponding locking slot portions of the inner implant member. The outer and inner implant members are preferably dimensioned for positioning between adjacent vertebral bodies.
In an alternative embodiment, the apparatus for facilitating fusion of adjacent vertebral portions includes an implant member dimensioned for positioning between adjacent vertebral portions and defining a longitudinal axis. The implant member includes an outer member having an exterior wall defining an internal cavity and a clip receiving opening subtending a peripheral portion of the exterior wall, an inner member telescopically received within the internal cavity of the outer member to permit relative movement of the outer and inner members and a locking clip dimensioned for at least partial reception within the clip receiving opening of the outer member. The inner member includes an exterior wall defining an internal cavity and has a plurality of locking slots spaced along the longitudinal axis. The locking clip includes a clip base and locking clip legs depending from opposed ends of the clip base. The locking clip legs include clip projections which are dimensioned for reception within corresponding locking slots of the inner member to selectively secure a relative position of the outer and inner members to establish a predetermined height of the implant member. The clip base of the locking clip may include a clip projection dimensioned for reception within a corresponding locking slot of the inner member. The inner member preferably includes a series of locking slots defined in the exterior wall thereof and spaced along the longitudinal axis. Each series includes a pair of spaced slot portions for reception of the locking clip legs and an intermediate slot portion for reception of the clip base.
The exterior wall of the outer member may include a plurality of perforations extending in communication with the internal cavity thereof to permit bone growth therethrough. Similarly, the exterior wall of the inner member may also include a plurality of perforations extending in communication with the internal cavity thereof to permit bone growth therethrough. An end cap may be releasably mounted to a longitudinal end of one of the inner and outer members. Bone growth inducing substances may be disposed within the internal cavities of the inner and outer members to facilitate bone ingrowth.
A method for supporting vertebral portions is also disclosed. The method includes the steps of accessing adjacent vertebral portions, providing an implant apparatus including an outer member having an exterior wall defining an internal cavity and an inner member telescopically received within the internal cavity of the outer member and having an exterior wall defining an internal cavity and a plurality of locking slots spaced along the longitudinal axis, extending the outer and inner members of the implant member to a predetermined length, positioning a locking clip within the clip receiving opening of the outer member whereby locking clip legs of the locking clip are received within corresponding locking slots of the inner member to selectively secure a relative position of the outer and inner members to establish a predetermined height of the implant member and introducing the implant apparatus within a space defined between two vertebral portions. An end cap may be mounted to exposed ends of the inner and outer members. Bone graft material may be introduced within the internal cavities to facilitate bone ingrowth.